LevelMatchFilter should return Neutral when no match is found
Currently the LevelMatchFilter returns either Accept or Deny explicitly when a match is not found. The return value is the opposite of the value returned when a match is found. In order to utilise the filter chaining the filter should return Neutral when no match is found, this allows additional filters to work on the event.
This is a breaking change for the LevelMatchFilter.
This will resynchronise the behaviour with log4j.